Downhole tools and methods for detecting a downhole obstruction within a wellbore

A method of detecting a downhole obstruction within a wellbore that extends between a surface region and a subsurface region, the method comprising:

• conveying a downhole tool though a first region of a wellbore including a gas;
• positioning the downhole tool within a second region of the wellbore including a liquid, wherein the second region is downhole from the first region, wherein a gas-liquid interface is defined between the first region and the second region, wherein the positioning includes positioning via a positioning mechanism of the downhole tool such that the liquid fluidly contacts at least a portion of the downhole tool, and wherein the positioning mechanism comprises a fluid analysis structure configured to detect when the liquid fluidly contacts the at least the portion of the downhole tool;
• and wherein the downhole tool comprises a controller programmed to control the operation of at least a portion of the downhole tool, wherein the positioning mechanism is configured to provide a position signal to the controller indicating that the downhole tool is positioned within the second region of the wellbore, and wherein the positioning further includes retaining the at least the portion of the downhole tool within the second region of the wellbore using an interface retention mechanism of the downhole tool that comprises a buoyancy-modifying structure configured to cause the at least the portion of the downhole tool to be buoyant downhole from the gas-liquid interface;
• generating an acoustic pulse with an acoustic pulse generator of the downhole tool, wherein the controller is programmed to initiate the acoustic pulse, with the acoustic pulse generator, based, at least in part, on the position signal;
• propagating the acoustic pulse within the liquid and at least partially in a downhole direction from the downhole tool;
• reflecting the acoustic pulse from a downhole obstruction to generate a reflected acoustic pulse, wherein the downhole obstruction is downhole from the downhole tool;
• propagating the reflected acoustic pulse within the liquid and in an uphole direction from the downhole obstruction;
• receiving the reflected acoustic pulse with an acoustic detector of a sensor assembly of the downhole tool;
• and
• characterizing the downhole obstruction based, at least in part, on the reflected acoustic pulse.